As the need for increased storage changes, the search for higher density, faster access memory technologies also increases. One of these, holographic data storage, provides the promise for increased access to higher density data. The techniques for realizing such storage typically utilize some type of storage media, such as photorefractive crystals or photopolymer layers, to store 3-D stacks of data in the form of pages of data. Typically, coherent light beams from lasers are utilized to perform the addressing, writing and reading of the data from the storage media by directing these beams at a specific region on the surface of the media. Writing is achieved by remembering the interference pattern formed by these beams at this region. Reading is achieved by detecting a reconstructed light beam as it exits the storage medium, the data then being extracted therefrom. Addressing is achieved by the positioning of the laser beams, and this is typically done through the mechanical movement of mirrors or lenses; however, the storage media itself can be moved relative to fixed laser beams.
One of the limiting aspects to the density of data stored in the storage media is the hardware complexity associated with the optics necessary for storing the number of pages in a given storage area within the holographic storage media, and therefore cost. Additionally, as the surface of the holographic media increases, both the size of the individual lenses utilized in the optics and the spacing therebetween will also increase. Both the complexity of the optics and the size of the various lenses required for large surface holographic media significantly increase cost. Typically, this is due to the fact that conventional optics systems that have been proposed for use with holographic storage media require various lenses to expand, collimate and deflect light beams. If one desired a holographic media with a surface as large as, for example, one meter, this could require lenses with diameters greater than one meter, given achievable F-numbers, and with spacings between two lenses that could exceed two to four meters. The overall train of optics could therefore extend over six meters. This, of course, is the precise problem that has confronted optics manufacturers in the field of astronomy. To solve these problems, they have resorted to spherical mirrors for collecting light and redirecting it to a viewing lens. However, these techniques have not been applied to holographic storage techniques.